1916] SOILS FERTILIZERS. 723 



to about 250°, after which it rapidly fell to a minimum. The increase in am- 

 monia was accompanied by a decrease in nitrates, which were practically non- 

 existent in the highly heated soils. . . . 



" The percentage of seed germination has been found to be closely correlated 

 with the amount of ammonia present in the heated soils studied. The amount 

 of ammonia required to injure germination, however, appears to vary with the 

 type of soil when comparisons of different heated soils are made. It appears 

 that the absorptive power of the soil is a very important limiting factor in 

 determining the extent of the injurious action. 



"The presence of dihydroxy stearic acid . . . could not be demonstrated In 

 the most toxic of the heated soils. That the toxic substance is of a volatile na- 

 ture is evidenced by the fact that it is readily removed from the soil by aera- 

 tion. . . . The evidence at hand points toward the formation and injurious 

 action of ammonium carbonates particularly. These salts being unstable In 

 the soil, except when kept in a dry and unaerated condition, accounts for the 

 gradual disappearance of the injurious action of heated soils. It also appears 

 that other compounds of ammonia are formed which are more stable in char- 

 acter. The beneficial action of heated soils on plant growth, especially of 

 those heated between 150 and 250°, is believed to be due in a large part to 

 the direct assimilation of ammonia or ammonium compounds by the plants." 



Chang-es in soils brought about by heating, Miss A. Wil.son (Notes Bot. 

 School Trinity Col Dublin, 2 (1916), No. 6, pp. 311-SlH, figs, 3).— The substance 

 of this article has been noted from another source (E. S. R., 34, p. 722). 



The occurrence of bacteria in frozen soil, E. C. Harder (Bot. Gaz., 61 (1916), 

 No. 6, pp. 507-517, figs. 2). — Experiments conducted at the University of "Wis- 

 consin with field and potted soil to determine the effect of cold and moisture on 

 bacterial numbers are reported. 



It was found that " the number of bacteria in surface soil increased markedly 

 after heavy frosts and in general maintained a high average during the winter 

 months. The increases and decreases, however, were found to bear a distinct 

 relation to the moisture content. The potted soils failed to show such marked 

 increase in bacterial content after frosts. On the contrary, the enriched cultures 

 showed a distinct retardation of bacterial growth when in a frozen condition. 

 The bacterial flora was more or less the same during the fall, winter, and 

 spring, with the exception that after heavy frosts the small transparent colonies 

 characteristic of water and of deeper soils formed a larger proportion of the 

 growth on the plates. 



" From these results it seems reasonable to conclude that ordinary soil bac- 

 teria undoubtedly withstand cold to a marked degree, even to temperatures as 

 low as 4° C. or more below zero. The increase in numbers, however, seems to 

 be due to mechanical transportation by moisture coming up from below during 

 heavy frost, and where such transportation is not possible there is an actual 

 retardation in grov/th as compared with that in unfrozen soils." 



Soil bacteria and phosphates, C. G. Hopkins and A. L. Whiting (Illinois 

 Sta. Bui. 190 (1916), pp. 393-406). — A general review of present knowledge of 

 the subject is given, together with the results of experiments on the solution of 

 rock phosphate by nitrite and nitrate forming bacteria. 



It was found that " nitrite bacteria make phosphorus and calcium soluble 

 from insoluble phosphates when they oxidize ammonia into nitrite. The actual 

 ratio found shows that about 1 lb. of phosphorus and about 2 lbs. of calcium are 

 made soluble for each pound of nitrogen oxidized, aside from the action of the 

 acid radicles associated with the ammonia. . . . Neither ammonia-producin'^ 

 67476°— 17 3 



